linux-kernel - Re: [PATCH] gpio: mcp23s08: Add option to configure pullups.

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Date:   Wed, 26 Oct 2016 11:59:14 +0200
From:   Enric Balletbo Serra <eballetbo@...il.com>
To:     Alexander Stein <alexander.stein@...tec-electronic.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH] gpio: mcp23s08: Add option to configure pullups.

Hi Linus,

2016-10-24 8:13 GMT+02:00 Alexander Stein
<alexander.stein@...tec-electronic.com>:
> On Monday 24 October 2016 02:53:31, Linus Walleij wrote:
>> On Fri, Oct 21, 2016 at 5:00 PM, Enric Balletbo i Serra
>>
>> <enric.balletbo@...labora.com> wrote:
>> > Default is without pullups, but if property is specified in DT and the bit
>> > is set, set a pullup on GPIO-n.
>> >
>> > Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
>>
>> I don't generally like this.
>>

I tried to use the same approach as used in gpio-twl4030.c because is
what I knew before. Maybe you can point me to a better approach?

>> In device tree it is the consumer that specifies how the line is used,
>> not the producer (gpiochip).
>>
>> We currently only specify polarity, open drain and open source
>> for consumers though.
>>
>> And the entire pin control system came into being *exactly* because
>> Grant didn't like me adding these things to the GPIO drivers.
>>
>> So how many other things does the MCP support? Drive strength?
>> Schmitt trigger? Is there a datasheet?
>
> Some unsupported features (AFAIK):
> * Input polarity (IPOL register)
> * open-drain interrupt pin
> * pullup on pins (proposed patch)
>
> Datasheet is here: http://ww1.microchip.com/downloads/en/DeviceDoc/21919e.pdf
>
> Best regards,
> Alexander
>
> --
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